That alterations in membrane structure and function are critical biochemical events in cell injury is a well accepted theme. This proposal details experiments which will further develop this thesis for nephrotoxic action to produce renal cell injury. It will focus on two critical membrane systems of the cell, the plasma membrane and the inner mitochondrial membrane. Disruption of these two membrane systems will result in disturbances in the intracellular ionic environment, diminished oxidative phosphorylation and declines in cell energy levels, disturbances felt to be instrumental in irreversible cell injury in other organ systems. The role of cellular and mitochondrial Ca++ overload in these processes will be clarified. Experiments are planned to characterize the permeability and transport alterations, especially to Ca++, occurring in isolated renal brush border membranes after in vivo and in vitro exposure to gentamicin, HgCl2, and cis-platinum. Experiments are planned to carefully delineate the precise effects of gentamicin, HgCl2 and platinum compounds on renal cortical mitochondrial function in vitro and compare them to the alterations observed after in vivo exposure in order to delineate direct vs. indirect effects. Measurement of nephrotoxin levels associated with mitochondria after in vivo exposure are planned to help in this assessment. Experiments are also planned in isolated proximal renal tubules from kidneys in early nephrotoxicity to determine if the mitochondrial alterations occur in situ within the cell as well as after isolation. Tissue and mitochondrial cation content, especially Ca++, will be measured in renal cortical tissue in early nephrotoxicity to shed light on the precise role of Ca++ overload in this disease state. Finally, competitive inhibitors of the gentamicin-renal cell surface receptor interaction will be employed to see whether they can ameliorate gentamicin nephrotoxicity.